[Lazarus] PageControl tabs not showing

[Werner Pamler]

The are two postings in the forum in which tabs of a pagecontrol do not 
show up if a TsSpreadsheetGrid or a TlzRichEdit are placed on the 
preceding tab at design-time:
- forum.lazarus.freepascal.org/index.php/topic,27088.msg167251.html 
(TsSpreadsheetGrid)
- forum.lazarus.freepascal.org/index.php/topic,26834.msg166016.html 
(TlzRichEdit)

I can confirm this issue on Laz trunk / fpc 2.6.4 on Win, the OP use Laz 
1.2.6 on Win/Ubuntu: Create a new form with a pagecontrol containing 
three tabs. Add a TsWorksheetGrid (or TlzRichEdit) on the first tab. Run 
-> there is only the first tab with the component added. Save and reload 
the project. Now again, there is only 1 tab also at designtime. Delete 
the WorksheetGrid/RichEdit, save and reload --> the three tabs are back.

If these controls are added at runtime, everything is ok.

Since other controls work fine on a PageControl these two components 
seem to miss something which prevents the other tabs to show up. Any 
idea what could be wrong?