@SlickTeam: Seems that the change in tagfind.e (timer callback 'updateSymbolPreview') reveals a problem which simply did't occur in v <= 12.02.
In my window/toolbar setup both TBs are docked at the bottom so only 1 is visible at a time. If I activate the symbol match list in the 'Find Symbol TB' the 'Preview TB' gets unintentionally activated (triggered by the timer).
This should solve this problem (at least it 'works for me'):
tagfind.e - updateSymbolPreview() [line 770]:
// HS2-CHG: do not force activation of Preview TB e.g. in case both are docked
// cb_refresh_output_tab(cm, true, true);
cb_refresh_output_tab(cm, true);
HS2
PS: 'Files TB' also/still shows this (wrong) behaviour as already reported time ago.