Inconsistent highlighting with ^S modifier

[gwsw]

Steps to reproduce:

1. Run seq 100 | less
2. Enter /(3)|(4) and press Enter.
3. Observe each 3 and 4 is highlighted.
4. Enter / ctrl-S 1 and press Enter.
5. Observe that each 3 and 4 remains highlighted.
6. Enter / ctrl-S 1 (3)|(4) and press Enter.

Expected result:
Each 3 and 4 remains highlighted.

Actual result:
Only the 3's are highlighted.

Tested with less-672 built with PCRE regular expressions.

[gwsw]

Fixed in b71a578.