Internal analog modem with lack of CTS on certain Linux systems

An issue was noticed on a Linux 3.5.0 system while running a MT5634ZPX-PCI-U modem. This issue may apply to other internal analog modems or to other analog modems.

The problem is that CTS from the modem was not being acknowledged on the Linux system.

The cause is from a specific commit in the official Linux kernel tree.
Commit 235dae5d094c415fcf0fc79fa637f1901bc8afe2, preceding v2.6.36-rc1 added support for STEricsson U6715 16650A UART causes this issue.

Undoing the commit (even in current kernels), corrects the problem.