G'day Jamie,
Thanks for the advice. Yes, a full cleanup & build makes no difference. All of the tabs work, but just not in the order of their tab stop number! Deleting an object that is jumped to and reinstating it causes the jump to move to the next component, so it is somewhat dynamic rather than fixed.
Weird behavior (no component is read only) but I have over 100 tabs on the form (is there a limit?). Tabbing goes (for example) 117, 118, 73, 119, 120 etc. When I look at the tab stop numbers they are all correct (ie 73 is 73 etc).
The platform is Windows 7 64 bit Lazarus is 1.6.4 FPC 3.0.2
DG