Prefixing properties with "Is" makes it obvious that they are booleans.
If you didn't know better, TabStop could be a number and get confused with TabIndex.
Using IsTabStop instead avoids this problem.
Grouping related properties by category rather than listing them alphabetically brings IsTabstop and TabIndex closer together but the grouping could do with being more granular. The categories are often a little broad.
In Windows Forms, TabStop and TabIndex are usually in the small category Behaviour.
In WPF, IsTabStop and TabIndex are often in the large category Other.