When operating in "Write First" mode and using byte-write enable, the output is invalid during the write operation. This occurs when the following conditions exist:
- Virtex-4 device is targeted.
- The write port operating mode is "Write First".
- Byte-write enable is used
- The port aspect ratios of read and write widths are not 1:1 (asymmetric).
This issue has been fixed in Block Memory Generator v3.1 Core available with ISE8.2i IP Update #1. Please use the latest core.