In general, and in orchids particularly, the secondary buds or bulbs can starting to vegetal way, if the temperature is more than it need (45-50° in greenhouse, for example)

Dear Marpha Telepova-Texier Esq.

The reason is ovules in ovary part close to stem are not fertilized owing to lag of pollen tubes penetration speed  to reach these ovules, since the fruit growth is so fast in the direction opposite to the direction of pollen grain tubes. Unfertilized ovule will be aborted. While fertilized ovules commenced to develop embryos, which create new apical dominance producing Auxins to furnish vascular bundles of well established xylem and phloem to import assimilate, to produce well testy flavor. Thanks         

Dear Caser Ghaafar Abdel,

This is the processes, named Apomixis - when without polinisation & fertilization plant developed the ovule !!!

Hi Caser,

[ Edit: I posted this to your another question. But actually my intention was to post it here for this question. Sorry for the confusion. ]

Please see the attached paper.

That can be induced by photoperiod, temperature and chemical treatment. Did any one of them applied in your observation of your onion plants?

From that paper:

1.  Alterations in organ initiation patterns, from floral to vegetative and back to floral, are characteristic of a reversion phenomenon.

2. "Reversion of flowering occurs when production of vegetative structures is resumed in a meristem after floral development has been initiated (Battey and Lyndon, 1990; Lyndon, 1998). It is possible for leaf production to resume at any time during flower initiation as long as the shoot apical meristem has not yet become completely determined for flower formation (Lyndon, 1990). Reversion is a result of changes in inductive and non-inductive stimuli that generate an initial, but insufficient, floral signal to maintain morphological floral development (Pouteau et al., 1997). Stimuli capable of evoking a reversion event include manipulations in photoperiod, temperature and chemical treatments."

Dear Yuan-Yeu Yau Esq.

Incomplete induction for conversion reversed the conversion in temperature requirements we call it devernalization, that means lag in the saturation requirements of conversion. So that you find a stem comes out of the middle flowers, or a apical turned to spines. This also  indeed with lack of imported assimilates.

@ Caser,

Thanks for mention the concept of 'Devernalization'. Below is a good site to read more about vernalization vs. devernalization.

http://plantcellbiology.masters.grkraj.org/html/Plant_Growth_And_Development11-Physiology_Of_Vernalization.htm

"Devernalization:

If vernalized seedlings or seeds are subjected to higher temperature like 35-40 oC the plants that develop from such treatment fail to flower.  Such a nullifying effect by higher temperatures is called Devernalization.  Nevertheless, if the vernalized plants are maintained at sufficiently low temperatures for a little long period of time, which has to be determined for every species, devernalization is not possible.  This may be due to the putative vernalin might have already moved and acted upon the genetic material and committed it in flower formation.  However, devernalized plants can be re-vernalized by subjecting the same seedling or seed again for another period of cold treatment by repetition of vernalization and devernalization cycles. "