Hello,
Please provide details regarding the custom field settings.
We suspect that you have set-up incorrect "values" for the custom field.
While you can enter almost whatever you want regarding the "text", the values need to be number or "namekeys" so they can be stored in the database and processed by PHP. The introduction of special characters generate unwanted side effects.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.